1. Field of the Invention
The invention relates to an apparatus for cooling plastic profiles, with a trough for receiving a cooling medium through which the profile can be guided and with several guiding means for calibrating the profile as well as with at least one inflow opening and with at least one outflow opening for the cooling water.
Plastic profiles are required as frame elements for windows or doors, for example. During their production, a plastic mass such as PVC is extruded at first through an opening corresponding to the profile. Immediately after the extrusion the profile has a doughy consistency. After the extruder an apparatus for dry calibration is usually provided, in which a first cooling and form stabilization is made. A further cooling process follows thereafter by means of a cooling medium, which is generally water, so as to carry off the heat from the inner regions of the profile. The invention relates in particular to such an apparatus for wet calibration.
2. Prior Art
There are known apparatuses of generally two types. A particularly efficient cooling is possible by the so-called spray bath. In this method the profile is guided through a trough which is equipped with a plurality of spray nozzles which are directed against the profile. Such an apparatus is very efficient, as the water jets hit the profile at high speed, thus ensuring favourable heat transmission. Moreover, in such an apparatus it is possible, by providing a favorable arrangement of the nozzles at sections of the profile which are difficult to cool such as re-entering angles or material accumulations, to cool at an increased level.
The spray bath is usually realized in a closed trough which is slightly evacuated during the operation. As in any case, atmospheric pressure prevails in the interior of the hollow profile, the vacuum causes the profile to sit close to the guiding means arranged at intervals within the trough and, thus, to be calibrated precisely. The vacuum is approximately between 0.1 to 0.3 bar and is produced by vacuum pumps which suck off air from the upper side of the trough.
The disadvantage in such a spray bath apparatus is the high consumption of water and the sensitivity of the nozzles. To achieve the optimal effect of such a spray bath, it is necessary to use nozzles of extremely small diameter. A feeding thereof with fresh water is generally not possible owing to the high water consumption. In the event that the water is recycled, however, extraordinary measures are required for water preparation. Despite these measures, blockages of the nozzles may occur, which may lead to deficient cooling of the profiles and the production of rejects.
The other known wet cooling system is the so-called full bath. In known apparatuses of this kind, the profile is guided through an upwardly open trough which is filled with a cooling medium such as water. In this system the supply of water is only required to the extent as is needed to regulate the temperature of the bath. Apparatuses according to said full bath principle are simple, easy to handle and consume little water.
However, until now it was not possible in a satisfactory manner to produce a pressure below atmospheric, similar to the spray bath, in the full bath. In addition to certain control-related problems, the formation of shock waves occur in certain operating conditions which lead to disadvantageous effects. This may reach right up to the destruction of the apparatus. Therefore, the quality of the calibration in known apparatuses according to the full bath principle is limited.